1. Field of the Invention
The present invention relates to an image reading apparatus and an image reading method.
2. Description of the Related Art
In recent years, a variety of apparatuses, such as a printer and what is called a multifunction product (MFP), that provide a function as a scanner are used. The MFP is an apparatus that functions as, e.g., a copier, a scanner, a facsimile machine, and a printer in a single casing; however, degradation in image quality can occur due to dirt, such as dust, sticking to a read surface of such an apparatus capable of scanning. Accordingly, various methods have been disclosed to prevent such degradation in image quality.
An example of such a technique is disclosed in Japanese Patent Application Laid-open No. 2006-229847. In this technique, an image reading apparatus includes a dust detecting unit. The dust detecting unit compares an image acquired by scanning with a normal image based on reference image data having been stored in advance, thereby determining whether a read surface is dirty. When it is determined that a value indicative of a level of dirtiness exceeds a threshold value, scanning is stopped and a notification that the read surface is dirty is provided to a user. When it is determined that the value is below the threshold value, various corrections such as shading correction is performed to the scanned-in image data depending on the level of dirtiness.
Scanning can be performed in any one of a sheet-fed mode and a flatbed mode. In the sheet-fed mode, scanning is performed by moving an original and fixing a carriage at a predetermined position. In the flatbed mode, scanning is performed by moving the carriage and fixing an original. The various corrections can be made in any one of these modes.
However, in the sheet-fed mode, when it is determined that image data has been acquired through a read surface to which the dust or the like is sticking, it is difficult to correct data (hereinafter, “vertical-streak-correction subject data”) that is a portion of the scanned-in image data corresponding to a portion where the dirt is present concurrent with image processing on the remainder of the image data (hereinafter, “image portion data”). Accordingly, in some cases, before the scanned-in image data is stored in a memory or the like as image data, the vertical-streak-correction subject data is divided from the image portion data. After the image portion data has been stored and subjected to the image processing, correction is made to the vertical-streak-correction subject data.
This technique will be described more specifically with reference to FIGS. 7A and 7B. FIG. 7A depicts exemplary image data to be processed by this technique. The image data acquired by a scanner by reading an original is divided into vertical-streak-correction subject data I11 and image portion data D11, D12, and then output to a memory or the like. The image portion data D11, D12 corresponds to portions where the no dirt is present. Referring to FIG. 7A, the image portion data D11 and D12 corresponds to portions where pixel values are relatively large while the vertical-streak-correction subject data I11 corresponds to a portion where pixel values are relatively small.
FIG. 7B is a schematic diagram depicting how the image portion data D11, D12 is processed. Before the image data depicted in FIG. 7A is stored in a memory M, the image data is divided into the image portion data D11 and D12 and the vertical-streak-correction subject data I11, which are then sequentially stored in the memory M and subjected to image processing. Correction is then made to the vertical-streak-correction subject data I11. Accordingly, in this technique, a relatively long period of time has inefficiently elapsed from the start of the scanning operation until its end, which has been a problem.